How to transfer latest state between threads in rust without using a mutex

I am working on a Rust project where I have two distinct threads that serve specific purposes. One is a real-time thread which interfaces directly with a piece of hardware and maintains strict timing requirements, while the other is a web server thread that provides an API for querying the current state of said hardware.

I need a mechanism through which the web server thread can acquire the most recent state of the hardware from the real-time thread. The challenge here is to avoid the use of mutexes, as the real-time thread cannot afford to be blocked waiting for the mutex.

Here are a few solutions I have considered and their corresponding challenges:

1. rwlock: But the writer thread (real-time thread) would need to wait if any reader has a lock on it.
2. Double Buffering: The thread that does the swap needs a mutable reference to the entire struct, which causes borrow checker problems.
3. mpsc Channel: If there are no web requests being made, the channel could fill up quickly, leading to wasted memory.

You can use the arc-swap crate, that provides the ArcSwap type (and related types): an Arc that can be replaced and loaded in a lock-free fashion.

I ended up using a ring channel with size 1, which uses a AtomicCell<Option<Box<T>>> from crossbeaml underneath.

The real-time thread can send() into the channel, which is atomic and lock-free. Then the web thread can recv() from the channel, or if there's nothing in the channel, continue using the last read value.